The present invention relates generally to electronic items identification systems and more particularly, to a radio frequency (RF) identification tag and method for identifying an item to or with which the tag is attached or associated, respectively, wherein each tag includes a plurality of circuits having a capacitance made up of a single capacitor and an individual made up of a single inductor coil which capacitor and inductor coil are in one-to-one correspondence such that each capacitor and inductor coil pair have a unique frequency at which the circuit resonates.
Currently, electronic item identification systems are in widespread use today to identify a variety of items. A first type of electronic item identification system commonly used in industry is one in which bar code labels are used to identify items. These types of electronic item identification systems are typically used by supermarkets, distributors, shipping services and clothing retailers to scan the bar code labels for quick retrieval of an item""s price or other information.
The way conventional bar code identification systems work is as follows. Bar codes labels are made up of a series of lines of varying widths or thicknesses to establish a code which can be read by a scanner. A bar code label is usually read by a laser scanner. The data from the scanner is electronically fed to a receiver which determines the identification code or number associated with the bar code label. The identification code or number is then sent to a central processing unit or computer where each code or number is matched to data stored on a master list such as item price or other information. The central processing unit or computer then electronically sends the stored data associated with the identification code or number to the cash register or other tabulator to arrive at a final total or tabulated result.
Another system of electronic item identification uses radio frequency (RF) identification tags to identify items. Radio frequency (RF) identification tags can be used to identify a variety of items to which the tags are attached or otherwise associated. In particular, radio frequency (RF) identification tags are currently used to identify passengers, luggage, library books, inventory items and other articles. Radio frequency (RF) identification tags will allow electronic identification of people or objects, moving or stationary, at distances of several feet.
In recent years, radio frequency identification tags have been manufactured using silicon chips. The silicon chips have been revolutionary because in the area of the size of the head of a pin, a silicon chip can hold a myriad of components and information. The problem with silicon chip radio frequency item identification tags is that silicon is very expensive and cannot be produced in the quantities necessary in industries such as the airline industry to make the tags feasible. Furthermore, the silicon chip identification tags are disadvantageous in having a limited range of approximately two feet and using a scanner that sends out only one signal which the chip alters by means of a phase shift. It would be desirable to develop a radio frequency identification tag that could be manufactured in mass quantities on a less expensive material than silicon such as paper or plastic and that could be used without having to alter the circuits on the tags in any way.
Other types of currently available radio frequency (RF) identification tags have the disadvantage that only recognition and surveillance functions can be performed. The radio frequency (RF) identification cards presently available in these types of systems do not to have the electronic properties necessary to allow for interrogation and identification functions.
For example, U.S. Pat. No. 4,694,283 to Reeb and U.S. Pat. No. 4,910,499 to Benge et al. both teach electronic identification systems which use multilayered radio frequency (RF) identification tags. The tags taught by the Reeb and Benge et al. patents each have conductive layers separated by a layer of di-electric material in order to form a resonant circuit. However, the Reeb patent teaches an electronic surveillance device and the Benge et al. patent teaches an anti-theft device, both of which are only usable for recognition and do not have the electronic properties necessary to allow for identification.
This is because the recognition function requires only one possibility, i.e., either resonant or not resonant. The identification function requires that the resonant frequency of the tag be read and then compared to another frequency to which it will match to achieve identification. It would be desirable for a radio frequency (RF) identification card to have the proper electronic properties to allow both recognition and identification functions to be performed with the card on an inexpensive material.
Some presently available radio frequency (RF) identification cards operate on the principle of establishing a code through the use of a pattern of binary numbers such as xe2x80x9conesxe2x80x9d and xe2x80x9czerosxe2x80x9d. These type of electronic item identification systems have the disadvantage that the radio frequency (RF) identification tag includes a circuitry for initially establishing a resonant circuit having a first resonating frequency which tag is activated by changing the resonating frequency of the resonant circuit to a second resonating frequency.
For instance, U.S. Pat. No. 5,218,189 to Hutchinson discloses a binary encoded multiple frequency RF identification tag and U.S. Pat. No. 5,103,210 to Rode et al. discloses an activatable/deactivatable security tag. The tags of both patents are used for identifying an item to which the tag is attached or with which the tag is associated. The tags both include an inductance connected in parallel with a capacitance wherein the capacitance is made up of a plurality of individual capacitors. The Hutchinson patent teaches individual capacitors which each have a predetermined different capacitance and which are connected in series and the Rode et al. patent teaches two capacitance branches which each have a predetermined different capacitance wherein the individual capacitors of each branch are connected in series.
In other words, according to the teachings of the Hutchinson and Rode et al. patents, the binary number generated from the circuit needs to be detected by varying the circuit""s total capacitance in order to check for resonance at a predetermined frequency. It would be desirable to develop an electronic item identification system using a radio frequency (RF) identification tag wherein each circuit on the tag has a constant inductance and capacitance and thus the circuit itself does not have to be changed to check for the resonating frequency.
The devices of the Hutchinson and Rode et al. patents short out capacitors during interrogation and thus the circuit can never be restored to its original frequency to be read over again. It would be desirable to develop an electronic item identification system in which the radio frequency (RF) identification tag can be read any number of times while still generating the same binary number as was read the first time and in this manner the tag can be reused.
The Hutchinson and Rode et al. patents teach a device where the binary number to be obtained from the tag must be predetermined. This is because the device teaches the xe2x80x9cdimplingxe2x80x9d of capacitors which to be accurate must be done with expensive, precision equipment. It would be desirable to develop an electronic item identification system in which a radio frequency (RF) identification tag having numerous circuits made up of capacitor/inductor coil pairs at evenly spaced intervals on the surface of the tag so that the presence or absence of a circuit or the circuit""s functionability could be programmed at the point of use with inexpensive equipment.
The present invention provides a radio frequency (RF) identification tag for identifying an item attached to or associated with the tag. The tag includes numerous circuits, C1 through CN, each having a capacitance and an inductance. The capacitance is formed by a single capacitor and the inductance is formed by a single inductor coil. The inductor coil is preferably wound around the capacitor to form a capacitor and inductor coil pair each of which have a unique resonant frequency. A scanner is used to transmit a frequency to the circuits. If any of the circuits located on the tag are resonant at the frequency transmitted, a binary number xe2x80x9c1xe2x80x9d is recorded for that circuit""s location. A circuit that is not resonant within the frequency range of the transmitted signal is given a binary number xe2x80x9c0xe2x80x9d and that circuit""s location is recorded. Once all circuits from C1 to CN have been scanned and assigned a binary xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d, a decimal number is calculated through the use of the binary table.